1. Field of Invention
This invention relates to reflective type active-matrix liquid crystal display devices and systems in which a liquid crystal layer is stacked on a driver layer formed on a semiconductor substrate.
2. Description of Related Art
Recently, liquid crystal displays have become widely used in various fields. In one type of liquid crystal display device, a liquid crystal layer is placed on and integrated with a driver layer formed on a semiconductor substrate. This type of liquid crystal display device is reflective and is combined with a light source for illuminating the front side of the display device to constructs a display system.
In the driver layer, a plurality of display elements, each including a transistor (a switching device) to drive a pixel electrode, are arranged in the form of a matrix on the semiconductor substrate. A pixel signal in accordance with an image signal is input to the display element and the output of the transistor in the display element drives the pixel electrode, whereby the molecular orientation of a portion of the liquid crystal on the pixel electrode (reflecting mirror) is controlled. As a result, the state of reflection of external light illuminating the pixel electrode is controlled in accordance with the pixel signal. By projecting the reflected light on a screen, the display system produces an image in accordance with the image signal.
For example, Japanese Patent Publication No. 2995725 (Laid-open Patent Hei 8-146458) discloses a liquid crystal display device formed on a semiconductor substrate in which shift in drain potentials caused by photo-carriers is minimized without adversely affecting the operation of pixel transistors.
FIG. 5 shows a conceptual sectional view of a known liquid crystal display. Referring to FIG. 5, a panel forming the liquid crystal display device includes a liquid crystal driver layer 102 formed on a surface of a silicon substrate 100 and a liquid crystal layer 104 formed over the liquid crystal driver layer 102.
The liquid crystal driver layer 102 formed on the surface of the silicon substrate 100 includes a switching transistor 106 having a source 106a, a drain 106b, and a gate 106c; a capacitor 108 containing a diffusion region 108a and an upper electrode 108b; and a pixel electrode (reflective mirror) 110 formed above the silicon substrate 100. The pixel electrode is connected to the drain 106b of the transistor 106, and is driven by an electric signal output at the drain.
The transistor 106 controls the orientation of portion of the liquid crystal on the corresponding pixel electrode 110. When a select line selects the transistor 106, the transistor 106 turns ON. While the transistor is ON, a pixel signal in accordance with an image signal is input to the source 106a. The signal is transferred to the drain 106b, and the output signal is thereby supplied to the pixel electrode 110 connected to the drain 106b. The output signal is also supplied to the upper electrode 108b of the capacitor 108. The capacitor 108 stores and maintains the output signal for a period during which the transistor 106 is OFF and minimizes a shift in the potential applied to the pixel electrode 110. As a result, an image can be stably displayed on the liquid crystal.
The size of the pixel represented by the size of the pixel electrode 110 ranges from 10 xcexcmxc3x9710 xcexcm to 30 xcexcmxc3x9730 xcexcm.
The liquid crystal layer 104 includes a liquid crystal 116 which is held between the pixel electrode 110 and a transparent electrode 114, and a glass plate 118 at the top.
A plurality of display elements each having the transistor 106, the capacitor 108 and the pixel electrode 110 are arranged in a form of an array on the silicon substrate 100 to form a display device. Each of the display elements is provided for each of the pixels. Controlling the pixel signal input to the pixel transistors 106 can control the orientation of portions of the liquid crystal 116 on the pixel electrodes 110. Therefore, when an incident light enters from the surface of the glass plate 118, an intensity of the light reflected by each of the pixel electrodes 110 is controlled by controlling the pixel signal. As a result, a desired image can be formed.
In order to improve the quality of the image, an increase in the number of pixels is required. To fulfill this requirement, an increased number of display elements should be arranged on a surface of a semiconductor substrate with a commercially acceptable area. As a result, a pixel size, or an area of the surface available for each display element becomes smaller. Because a high voltage is required to control the molecular orientation of the liquid crystal, however, the size of the transistor in the display element cannot become miniaturized even with an advance of the semiconductor fabrication process technology. Thus, the area that is provided for forming the capacitor tends to be decreased. The reduction of the area of the capacitor and resulting reduction of the capacitance to store the output signal may result in an instability of the image.
In order to solve the problems described above, it is an object of this invention to provide a display device and a display system including the display device that provides a sufficient area for capacitors even when the pixel size is reduced.
An exemplary embodiment of the display device according to the invention comprises an array of display elements arranged in a first and a second direction. Each of the display elements comprises a transistor including a source and a drain diffusion region formed in the surface of the semiconductor substrate, a capacitor, and a pixel electrode disposed over the surface of the semiconductor substrate. The drain diffusion region outputs an output signal, the capacitor stores the output signal, and the pixel electrode is driven by the output signal. The capacitor comprises a capacitor diffusion region formed in the surface of the semiconductor substrate, an insulating film disposed on the capacitor diffusion region, and a capacitor electrode disposed on the insulating film.
The array of display elements includes a first display element, a second display element arranged adjacent to the first display element in the second direction, and a third display element arranged adjacent to the second display element in the second direction. And the capacitor diffusion regions of the first and the second display elements extend along at least substantially an entire length of a border between the first and the second display elements and merge with each other at the border.
Preferably, an entire area of the surface of the semiconductor substrate provided for forming the first display element has a same conduction type before forming the capacitor diffusion region.
Preferably, the capacitor diffusion region of the first display element has a first conduction type and is formed in the surface of the semiconductor substrate having the first conduction type.
Other exemplary embodiments of the display devices according to this invention comprise an array of display elements arranged in a first and a second direction. The array of display elements includes a first display element, a second display element arranged adjacent to the first display element in the second direction, a third display element arranged adjacent to the second display element in the second direction. The array further includes a fourth display element arranged adjacent to the first display element in the first direction and a fifth display element arranged adjacent to the second display element in the first direction, the fourth and the fifth display element are arranged adjacent with each other in the second direction. The capacitor diffusion regions of the first, the second, the fourth and the fifth display elements merge with each other; and a contact to supply an electric potential to these capacitor diffusion regions is provided at a position surrounded by the capacitor electrodes of the first, the second, the fourth, and the fifth display elements.
Preferably, the capacitor electrodes of the first and the second display elements extend along substantially the entire length of the border between the first and the second display elements.
Other exemplary embodiments of the display devices according to this invention comprise an array of display elements arranged in a first and a second direction. The array of display elements includes a first display element, a second display element arranged adjacent to the first display element in the second direction, and a third display element arranged adjacent to the second display element in the second direction. The transistors of the second and the third display elements share a common gate electrode extending in the second direction beyond a border between the second and the third display elements.
Preferably, the array of display elements includes a select line to select display elements arranged in the second direction including the first, the second, and the third display elements; and the select line includes the common gate electrode and a wiring connected to the common gate electrode. The wiring extends in the second direction over the capacitor electrodes of the first and the second display elements.
Preferably, the array of the display elements includes a plurality of signal lines extending in the first direction to input pixel signals to the display elements.
Other exemplary embodiments of the display devices according to this invention comprise an array of display elements arranged in a first and a second direction. The array of display elements includes a first display element, a second display element arranged adjacent to the first display element in the second direction, and a third display element arranged adjacent to the second display element in the second direction. And the array of display elements includes a select line to select display elements arranged in the second direction including the first, the second, and the third display elements. The select line includes a wiring extending in the second direction over the capacitor electrodes of the first and the second display elements.